Vertebral compression fractures, as illustrated in FIG. 1, represent a generally common spinal injury and may result in prolonged disability. F. Margerl et al: A comprehensive classification of thoracic and lumbar injuries, Eur Spine J 184-201, 1994. These fractures involve collapsing of one or more vertebral bodies 25 in the spine. Compression fractures of the spine usually occur in the lower vertebrae of the thoracic spine or the upper vertebra of the lumbar spine. They generally involve fracture of the anterior portion of the affected vertebra 25 (as opposed to the posterior side). Spinal compression fractures can result in increased kyphotic deformation of the normal alignment or curvature of vertebral bodies in the affected area of the spine. Spinal compression fractures and/or related spinal deformities can result, for example, from metastatic diseases of the spine, from trauma or can be associated with osteoporosis.
Several minimally invasive surgical (MIS) procedures for treating vertebral compression fractures have been developed and tested with various degrees of success. These procedures generally involve the use of a cannula or other access tool inserted into the posterior of the effected vertebral body through the pedicles. The most basic of these procedures is vertebroplasty, which literally means fixing the vertebral body, and may be done with or without first repositioning the bone to restore the original height of the collapsed vertebral body.
In such MIS procedures, a cannula or special bone needle is typically passed through the soft tissues of the back. X-ray image guidance may allow the position of the needle to be seen at all times. Once the need is positioned, a small amount of polymethylmethacrylate (PMMA) or other appropriate orthopedic cement is pushed through the needle into the vertebral body. PMMA, the most common material used today, is a medical grade substance that has been used for many years in a variety of orthopedic procedures. Generally, the cement is mixed with an antibiotic to reduce the risk of infection, and a radiopaque powder containing barium sulfate, zirconium oxide or tantalum to allow it to be seen on X-ray.
Vertebroplasty is a treatment for vertebral compression, which can be effective in the treatment of fracture pain, the prevention of further collapse, and a return to mobility in patients. However, height restoration is an optional step of this procedure and thus, spinal deformity might not be addressed. Another treatment is balloon kyphoplasty, in which a catheter having an expandable balloon tip is inserted through a cannula, sheath or other introducer into a central portion of a fractured vertebral body. Kyphoplasty, by expanding the balloon in situ within the vertebral body, may potentially achieve the reconstruction of the appropriate lordosis, or normal curvature of the spine. The balloon is removed, leaving a void within the vertebral body, and PMMA or other filler material is then injected through the cannula into the void as described above with respect to vertebroplasty. The cannula is removed and the cement cures to fill or fix the bone. One potential disadvantage with this procedure is that when the balloon is removed the vertebral body may return to its collapsed position.
Another approach for treating vertebral compression fractures is a mesh-based system that provides material delivery using an expandable mesh graft balloon, or containment device, within the involved vertebral body. The balloon graft remains inside the vertebral body after its inflation, which reduces the chance of resettling, such as can occur during a kyphoplasty procedure when the balloon is withdrawn.
Still another procedure used in the treatment of vertebral compression fractures is an expandable polymeric slotted tube mass known as a Sky Bone Expander. This device can be expanded by compressing said tube longitudinally, increasing the slotted tube's diameter, but like kyphoplasty, once vertebral height is restored, the Sky Bone Expander is removed allowing for possible settling prior to cement injection and curing.
A proposed improved procedure for repositioning and augmenting vertebral body compression fractures is vertebral body stenting, for example as described in Furderer et al., “Vertebral body stenting”, Orthopade 31:356-361, 2002; European Patent number EP1308134B1; and United States Patent Application publication numbers US2003/0088249 and/or US2009/0069850, each of which is incorporated by reference herein in its entirety. Vertebral body stenting generally involves inserting into a vertebral body a balloon-tipped catheter surrounded by a stent. After insertion of the balloon and stent, the balloon is inflated, e.g., using fluid pressure, thereby expanding the stent within the vertebral body. After expansion of the stent, the balloon may be deflated and removed, with the stent remaining inside the vertebral body in an expanded state, defining a cavity to be filled with bone cement.
Another proposed improved procedure for repositioning and augmenting vertebral body compression fractures is the implementation of a porous or permeable containment device, as is described in PCT application WO2009064847, the contents of which are incorporated herein in their entirety. The porous containment device is inserted into the interior volume of a targeted vertebral body for restoring the anatomy of the bone, and is expandable by filling with, for example, a bone filler material. The containment device preferably permits the bone filler material to flow out of the containment device through one or more pores or flow-directing tentacles such that the bone filler material interdigitates with the surrounding bone tissue. The porous containment device is then de-docked from its insertion catheter and remains within the interior of the vertebral body.
While the concepts of vertebral body stenting and porous containment vertebral augmentation provide promise over other known methods for treating compression fractures, there remains a need for improved methods for repositioning, restoring height, and augmenting fractured vertebral bodies in any of the above-mentioned vertebral body augmentation procedures and potentially other bone augmentation procedures. One of the main goals of vertebral body augmentation procedures is the restoration of height to the collapsed vertebral body; however, such height restoration can only be achieved if the fractured portions of the vertebral body are mobile with respect to one another, as during the healing process hard bone, comparable to the compact cortical shell of the vertebral body, begins to fuse about and over the fractured region, especially in fast-healing younger patients whose injuries are the result of trauma (as opposed to severely osteoporotic elderly patients). Once the fractured portions of the vertebral body begin to fuse to one another in a collapsed configuration, height restoration may be impossible to achieve without resorting to more invasive means (e.g., osteotomy in which the fused bone is cut to provide bone fragment mobility again).
As can be appreciated, there is a wide variety of potential procedures as well as a wide variety of potential bone conditions; and each bone condition will not respond the same to the various procedures.